(1) Field of the Invention
The present invention relates to an imaging device (such as a digital camera or a digital video camera) and an image processing device that have a function to detect face regions of objects, and relates to a control method of the devices.
(2) Description of the Related Art
Proposed by some of conventional imaging devices are technologies of detecting a face region from a photographed image based on a predetermined algorithm, and performing various processes onto the detected face region by regarding it as the main object.
For example, Patent Document 1 discloses an automatic focus control (hereinafter referred to as AF control) performed onto a detected face region. Also, Patent Document 2 discloses setting imaging conditions, such as an automatic exposure control (hereinafter referred to as AE control), based on the detected face region, as well as the AF control.
The following describes the flow of a conventional AF control process with face detection.
First, the imaging device performs a face detection process when it is in a face detection operation mode. Methods of detecting faces are disclosed in, for example, Non-patent Documents 1 through 3, which Patent Document 1 refers to.
After detecting faces in the face detection process, the imaging device checks whether a plurality of faces have been detected. The imaging device performs a single face process when a single face has been detected. And when a plurality of faces have been detected, the imaging device checks whether a distance measuring area selection mode, which a target face for the AF control is selected by user operation, has been set. When the distance measuring area selection mode has been set, the imaging device displays a GUI on the liquid crystal monitor so that the user can select a face. The user selects a face that should be subjected to the AF control. The imaging device sets a distance measuring area to the user-selected face, and performs the AF control onto the distance measuring area. When the distance measuring area selection mode has not been set, the imaging device sets the distance measuring area to a face that is closest to the center of the image, and performs the AF control onto the face.
As described above, when an imaging device using such a conventional face detection method has detected a plurality of faces, it selects, as the face of the main object, a face that is closest to the center of the image or makes the user select a face among them.
Patent Document 1: Japanese Patent Application Publication No. 2003-107335
Patent Document 2: Japanese Patent Application Publication No. 2003-127489
Non-patent Document 1: “A Proposal of the Modified HSV Colour System Suitable for Human Face Extraction”, the Journal of the Institute of Television Engineers of Japan, Vol. 49, No. 6, pp. 787-797, 1995
Non-patent Document 2: “Extraction of Face Regions from Monochromatic Photographs”, the Journal of IEICE, Vol. J74-D-II, No. 11, pp. 1625-1627, November 1991
Non-patent Document 3: “Face region detection for television phone and its effects”, Image Lab, November 1991, Japan Industrial Publishing Co., Ltd.